1. Field of the Invention
The present invention relates to a multilayer ceramic electronic component and a method for producing the same, and an electronic component aggregate which is produced during a process for producing the multilayer ceramic electronic component. More particularly, the present invention relates to an improvement in a structure for mounting a cover on the body of a multilayer ceramic electronic component including the cover.
2. Description of the Related Art
Various types of multilayer ceramic electronic components which are of interest with regard to the present invention are shown in FIGS. 14 and 15.
A multilayer ceramic electronic component 1 shown in FIG. 14 includes an electronic component body 2, with external terminal electrodes 3 being disposed at side surfaces of the electronic component body 2. The electronic component body 2 has a structure in which a plurality of ceramic layers are stacked. Although a conductive film and a via hole conductor are provided as internal circuit conductors inside the electronic component body 2, these are not shown in FIG. 14.
When the multilayer ceramic electronic component 1 is mounted onto a wiring substrate 4, the external terminal electrodes 3 are connected to connection lands 5, disposed on the wiring substrate 4, through solder 6. Here, since the external terminal electrodes 3 are disposed on side surfaces of the electronic component body 2, the solder 6 forms a solder fillet.
A multilayer ceramic electronic component 11 shown in FIG. 15 includes an electronic component body 12, with external terminal electrodes 14 being disposed on a downwardly facing major surface 13 of the electronic component body 12. The electronic component body 12 has a structure in which a plurality of ceramic layers 15 are stacked, and an internal circuit conductive film 16 and an internal circuit via hole conductor 17 are provided as internal circuit conductors inside the electronic component body 12.
The external terminal electrodes 14 are called LGA (land grid array) type electrodes. When an attempt is made to mount the multilayer ceramic electronic component 11 onto the wiring substrate 4, the external terminal electrodes 14 are arranged so as to oppose connection lands 5 on the wiring substrate 4, and the external terminal electrodes 14 and the connection lands 5 are connected together through solder 18. In soldering using the solder 18, ordinarily, cream solder is printed onto the connection lands 5, and, then, the multilayer ceramic electronic component 11 is placed onto the wiring substrate 4 in order to carry out reflow soldering using the cream solder. Unlike the multilayer ceramic electronic component 1 having the external terminal electrodes 3 disposed on side surfaces of the electronic component body 2 shown in FIG. 14, the multilayer ceramic electronic component 11 including the LGA-type external terminal electrodes 14 shown in FIG. 15 is such that the planar dimensions of the multilayer ceramic electronic component 11 itself becomes a planar dimensions that is required for mounting because the solder 18 does not form a solder fillet. Consequently, the planar dimensions required for mounting can be made small, so that higher density mounting can be achieved.
Electronic components which cannot be incorporated inside the electronic component body 2 of such a multilayer ceramic electronic component 1 or the electronic component body 12 of such a multilayer ceramic electronic component 11, such as inductors, capacitors, resistors, transistors, diodes, or integrated circuits, are sometimes mounted onto an upwardly facing major surface of the electronic component body 2 or the electronic component body 12. In FIG. 14, these components that are mounted are not shown. In FIG. 15, a number of components 20 that are mounted are shown on an upwardly facing major surface 19 of the electronic component body 12.
When such components 20 are mounted, for the purpose of, for example, causing the multilayer ceramic electronic component 1 or the multilayer ceramic electronic component 11 to be in a surface mountable state, a cover 7 (indicated by broken lines in FIG. 14) or a cover 21 (indicated by broken lines in FIG. 15) is joined to the electronic component body 2 or the electronic component body 12 corresponding thereto. The covers 7 and 21 are like receptacles, and are arranged so that their openings face their corresponding electronic component bodies 2 and 12.
In the case of the multilayer ceramic electronic component 1 shown in FIG. 14, when the cover 7 is made of metal, it can be secured to the electronic component body 2 by, for example, soldering and joining it to either one of the external terminal electrodes 3.
In contrast, in the multilayer ceramic electronic component 11 shown in FIG. 15, since the external terminal electrodes are not disposed on side surfaces of the electronic component body 12, the cover 21 cannot be easily mounted as the cover 7 can in the multilayer ceramic electronic component 1 described above.
For example, when an attempt is made to mount the cover 21 using the downwardly facing external terminal electrodes 14 mounted to the electronic component body 12, the planar configuration of the multilayer ceramic electronic component 11 becomes larger than the planar size of the electronic component body 12 by an amount corresponding to the thickness of the cover 21 and a joining portion to the external terminal electrodes 14, thereby preventing size reduction of the multilayer ceramic electronic component 11.
There is a method illustrated in FIG. 16. In this method, joining electrodes 22 are disposed on the upwardly facing major surface 19 of the electronic component body 12, end portions 23 defining the opening of the cover 21 are bent inward so as to oppose the joining electrodes 22, and the end portions 23 are soldered to the joining electrodes 22 using solder 24.
However, when such a method described above is used, since the area for mounting the components 20 onto the major surface 19 of the electronic component body 12 becomes small, in order to cause this mounting area to be equal to or greater than a certain area, the multilayer ceramic electronic component 11 must be made rather large.
When the cover 21 is made of metal, the area of the bent end portions 23 cannot be made so small due to processing problems. In addition, in order to provide the required adhesive strength between the joining electrodes 22 and the end portions 23, the areas of the joining electrodes 22 and the areas of the end portions 23 cannot be made so small. Therefore, regardless of the planar size of the electronic component body 12, the areas of the joining electrodes 22 and the areas of the end portions 23 need to be equal to or greater than certain areas. The smaller the planar configuration of the electronic component body 22, the more noticeable the problem concerning restrictions on the area for mounting the aforementioned components 20 becomes.
On the other hand, an electrode shown in FIG. 17 has been proposed as an electrode disposed on a side surface of an electronic component body of a multilayer ceramic electronic component. FIG. 17 is a perspective view showing in enlarged form a portion of an electronic component body 26 of a multilayer ceramic electronic component 25. A notch 28 which vertically passes through the electronic component body 26 is disposed in a side surface 27 of the electronic component body 26. An electrode 29 is arranged so as to cover the inside surface defining the notch 28.
The aforementioned electrode 29 may, for example, be formed by a method such as the following.
Basically, in this method, after forming an electronic component aggregate from which a plurality of the electronic component bodies 26 are obtained, the electronic component aggregate is divided along predetermined division lines in order to obtain the electronic component bodies 26.
More specifically, an electronic component aggregate having a structure in which a plurality of ceramic layers are stacked is formed. Either before or after baking, through holes, which become notches 28, are formed in the electronic component aggregate. Conductors, which become electrodes 29, are provided at the inside surfaces defining the corresponding through holes. Typically, electrically conductive paste is used as the conductors. When the electrically conductive paste is applied, the electrically conductive paste is usually applied to both peripheral portions of the openings of the through holes.
Next, after baking, the electronic component aggregate is divided along division lines that pass through the through holes. Surfaces which are formed as a result of this dividing operation become side surfaces 27. The through holes are divided and become the notches 28. The conductors applied to the inside surfaces defining the through holes are divided and become the electrodes 29.
However, the above-described method has the following problems.
When the electronic component aggregate is divided, what is called chocolate breaking is usually performed. During the dividing operation, the conductors may not be properly divided. As a result, a portion of the electrode 29 inside the notch 28 of one divided electronic component body 26 may be “forcefully transferred” to the electrode 29 inside the notch 28 of another electronic component body 26. In extreme cases, an electrode 29 may not be formed inside the notch 28 of the one electronic component body 26.
In order to overcome this problem, it is necessary to apply the conductors to the inside surfaces defining their corresponding through holes as thinly and uniformly as possible. However, it is relatively difficult to uniformly and thinly apply the conductors.
Another method is carried out instead of the above-described method. In this method, before placing upon each other a plurality of ceramic green sheets forming a raw electronic component aggregate, through holes are formed in the ceramic green sheets and conductors are applied to the inside surfaces defining the through holes. In this case, after forming the through holes and applying the conductors to the inside surfaces defining the through holes, the plurality of ceramic green sheets are stacked and pressed in a stacking direction. By this process, a raw electronic component aggregate is produced, and is baked.
However, even when this method is used, since a plurality of electronic component bodies 26 are obtained by dividing the electronic component aggregate, the same problems as those of the above-described method are encountered. In addition, since the ceramic green sheets having through holes are stacked and pressed, other problems may be encountered. For example, the holes formed in each of the ceramic green sheets may become undesirably deformed due the heat and pressure applied in the pressing step, or positional displacements of through holes with respect to each other may occur in the stacking step.